Methods to prevent wheel slip in an autonomous floor cleaner

ABSTRACT

Tread structures, wave motion navigational controls, and ramp up recovery controls are provided to an autonomous floor cleaner to reduce wheel slippage. The floor cleaner delivers liquid to the floor as part of the cleaning process. Wheels on the device are provided with relatively deep peripheral grooves to minimize the contact surfaces of a sprocket wheel and to accommodate the layer of liquid on the floor. In the event of wheel slippage, or to prevent wheel slippage, the device is designed to move forward with a slight side-to-side wave action caused by periodically altering the relative speeds of two drive wheels. There is also provided a slippage recovery mode where the drive wheels shut down or greatly slow when severe slippage is sensed, followed by a slow ramp up of speed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application that claims benefitto U.S. patent application Ser. No. 11/168,038 filed on Jun. 28, 2005.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not applicable

BACKGROUND OF THE INVENTION

It is desirable to minimize the amount of human labor expended inmaintaining and cleaning buildings. The art has therefore developedautonomous robotic devices that can clean or otherwise maintain or treathard floors, carpeting and similar surfaces without the necessity for ahuman to be present during the operation of the device.

In some such devices a liquid is applied to the flooring area beingtreated. For example, U.S. Pat. No. 5,279,672 discloses a roboticcleaning apparatus where a cleaning solution is dispensed to the floorby a scrub deck. In U.S. Pat. No. 6,741,054 there is disclosed anautonomous floor mopping apparatus where cleaning fluid is applied tothe floor by way of a pre-moistened towel.

Such robotic devices typically have a programmable controller fordirecting the device in a preferred movement pattern. This helps insurecoverage of the full area to be treated, as well as helping to insurethat obstacles (e.g. furniture legs) and undesired contact points (e.g.stairways) are avoided. The controllers are typically linked to motorsthat drive the wheels of the device on the floor.

While devices of this type can work quite well on dry surfaces, thewheels of such devices may slip when traveling over areas of the floorthat are wet from the fluid being applied. This is particularly likelywhen the liquid itself is of the type which, when wet, is significantlymore slippery than water (e.g. contains oil for polishing purposes).Such slipping can cause the device to remain in place for an extendedperiod, or more likely cause the device to divert in an unexpecteddirection from the optimal desired path. This can extend the time neededto treat the surface, and/or can lead to portions of the surface notbeing adequately treated.

In some robotic devices, a third wheel that is not driven by a motor isused to monitor the movement of the robot. This third wheel has anoptical or mechanical sensor (encoder) that will send a digital signalto the controller as long as the robot is moving. Hence, if the robot isin a moving mode, but this third wheel does not sense movement, then thecontroller knows it is slipping. This method detects slip. This thirdwheel may be called a stator wheel.

In connection with automobile and truck tires there has been substantialwork on trying to improve the traction of the tires through the use ofvaried tread patterns. However, many of these approaches are designed totake advantage of the very heavy weight of such vehicles, and are noteasily transferred to environments where a cleaning robot is involvedthat weighs much less. Others of these approaches rely on expensivematerials, or structures that are relatively expensive to create.

Similarly, in connection with automobiles and trucks, there have beenattempts to provide improved anti-slip control by monitoring wheelmovement and automatically altering power to the wheels when sensingsuch slip. Because such controller systems were designed for extremelyheavy vehicles, they were not easily transferred to environments where acleaning robot was involved that weighed much less. Further, somesystems that could be transferred to a small cleaning robot were of toogreat a cost to be used in that environment as a practical matter.

Hence, a need still exists for improved structures and systems foraddressing wheel slip concerns in the context of an autonomous floorcleaner.

BRIEF SUMMARY OF THE INVENTION

The invention addresses the foregoing needs by modifying the wheelstructure to provide radial transverse recesses of substantial depthbetween gear-like teeth, by providing a side-to-side wave pattern forforward motion of the device, and/or by providing a reset and ramp upmode once severe wheel slippage is sensed.

During a wet treating operation, a thin film of fluid (e.g. cleaningfluid) is deposited on the floor surface. The maximum layer thickness iscontrolled so as not to be greater than the depth of radial transversechannels on the wheel. This can be achieved by first applying the liquidto an application cloth, and then controlling the amount of liquid onthe cloth and the speed of take-up of the cloth relative to devicemovement. It can also be achieved by directly applying liquid to thefloor, but in a manner where the amount of liquid dispensed is limitedbased on the area that the device passes over.

In connection with such a tread design, it is desirable to make thecontact area of the tire as small as possible, so that more of theweight of the device is borne in a small area of contact. This helpsdrive the contact surface down through any pooling liquid. A preferredway to achieve this is to form the tire in a sprocket shape with theradial edges of the sprocket being very small rectangular areas. Such astructure also has advantages for gripping a carpet.

A particularly preferred form of wheel can be molded from athermoplastic elastomer. Such materials are particularly suitable forinexpensive injection molding.

Applying this approach to the invention, there is provided a roboticdevice for treating (e.g. preferably cleaning) a surface wherein therobotic device includes means for reducing the incidence of wheel slip.The robotic device has a wheel having a tread which has sprocket teethseparated by a radially extending peripheral groove. The peripheralgrooves are of a depth exceeding 0.15 cm. The sprocket teeth aresuitable to contact the surface being treated.

The robotic device has a housing supported by the wheel, and means fordelivering a layer of fluid onto the surface. The robotic device alsohas a controller in communication with the means for delivering a fluid.The controller provides fluid delivery signals to the means fordelivering a fluid such that the layer of fluid can be provided on thesurface being treated having a thickness not exceeding the peripheralgroove depth.

In another aspect the invention provides a robotic floor treater thatdelivers a liquid to the floor. The treater has a navigation patterncomprising a side-to-side wave pattern. This is preferably achieved byperiodically changing the wheel speed of at least one wheel, andpreferably of at least two wheels. The device can be designed, when itis moving forward, to move a short distance (e.g. 1 cm) to the right,followed by movement a short distance to the left. The cycle is repeatedcontinuously. Alternatively, the wave pattern can be initiated onlyafter a certain degree of slippage is sensed.

Adopting such a wave pattern has been surprisingly found to reduce theincidence of wheel slippage, and/or help the device recover fromslippage once it occurs. Because the side-to-side movements are sosmall, this can be achieved with disrupting the ability of the device toessentially move linearly (e.g. along a wall).

In yet another aspect an autonomous robotic device has a first wheeldriven by a first motor, a second wheel driven by a second motor, and ahousing supported by the wheels. The robotic device further includesmeans for measuring wheel rotation for the first wheel and the secondwheel.

In one preferred form the means for measuring wheel rotation is anencoder. The controller receives first wheel rotation signals associatedwith the first wheel and second wheel rotation signals associated withthe second wheel from the means for measuring wheel rotation. Thecontroller outputs first speed signals to the first motor for drivingthe first wheel and second speed signals to the second motor for drivingthe second wheel. The controller executes a stored program to calculatea first amount of slip for the first wheel from the first wheel rotationsignals received from the means for measuring wheel rotation andcalculate a second amount of slip for the second wheel from the secondwheel rotation signals received from the means for measuring wheelrotation.

When the first amount of slip exceeds a predetermined first value ofslip or the second amount of slip exceeds a predetermined second valueof slip, the controller provides first speed signals to the first motorand/or provides second speed signals to the second motor such that thedevice navigates in a side-to-side wavy pattern. This can be achieved byvarying relative wheel speed between the left wheel and the right wheelin a periodic fashion.

In still another embodiment such a robotic device for treating a floorhas a software routine that works in conjunction with speed signals fromthe wheels of the autonomous floor cleaner to reduce the speed of thewheels (e.g. stop the wheels) in the situation where the wheels areslipping too much on a wet surface. Once the anti-slip routine isimplemented and the wheels have either stopped or greatly slowed, theroutine will cause the wheel speed to ramp up in a slow manner. Thisallows the machine to try to recover at a slow speed, rather than justspinning slipping wheels at a slow speed.

The nature of the ramp up may be affected by the cleanliness of thefloor or the amount of liquid used. Hence, the machine may be programmedto ramp up more slowly when a high level of liquid is known to bepresent. Further, in such a situation the device can go to a dead stopbefore ramping up, rather than merely a slowed speed.

This latter software system may be particularly effective when theliquid being applied is formulated for quick evaporation. By stoppingthe device one gives an opportunity for some of the liquid causing theslippage to evaporate.

It should be noted that the above tread designs, wave patterns, and rampup recovery software not only provide anti-slip assistance for wetfloors, they are of assistance when the floors are slippery due to thepresence of sand or other similar solid material.

In still another aspect the invention provides a robotic device fortreating a surface wherein the robotic device includes a first wheeldriven by a first motor, a second wheel driven by a second motor, and ahousing supported by the first wheel and the second wheel. The roboticdevice further includes an encoder for measuring wheel rotation for thefirst wheel and the second wheel. The robotic device has a controller incommunication with the first motor, the second motor, and the means formeasuring wheel rotation. The controller receives first wheel rotationsignals associated with the first wheel and second wheel rotationsignals associated with the second wheel from the means for measuringwheel rotation. The controller also provides first speed signals to thefirst motor for driving the first wheel and second speed signals to thesecond motor for driving the second wheel.

During operation of the robotic device, the controller executes a storedprogram to calculate a first amount of slip for the first wheel from thefirst wheel rotation signals received from the means for measuring wheelrotation and calculate a second amount of slip for the second wheel fromthe second wheel rotation signals received from the means for measuringwheel rotation. The controller then provides first speed signals to thefirst motor that slow or stop the first wheel if the first amount ofslip exceeds a predetermined first value of slip. The controller mayalso provide further first speed signals to the first motor thatincreases speed of the first wheel if the first wheel has been slowed orstopped because the first amount of slip has exceeded the predeterminedfirst value of slip.

In still another aspect, the invention provides a robotic device fortreating a surface wherein the robotic device includes means forreducing and/or preventing wheel slip. The robotic device has a firstwheel driven by a first motor, a second wheel driven by a second motor,and a housing supported by the first wheel and the second wheel. Therobotic device further includes means for measuring wheel rotation forthe first wheel and the second wheel such as an encoder. The roboticdevice also includes a controller in communication with the first motor,the second motor, and the means for measuring wheel rotation. Thecontroller receives first wheel rotation signals associated with thefirst wheel and second wheel rotation signals associated with the secondwheel from the means for measuring wheel rotation. The controllerprovides first speed signals to the first motor for driving the firstwheel and second speed signals to the second motor for driving thesecond wheel.

During operation of the robotic device, the controller executes a storedprogram to calculate a first amount of slip for the first wheel from thefirst wheel rotation signals received from the means for measuring wheelrotation, and calculate a second amount of slip for the second wheelfrom the second wheel rotation signals received from the means formeasuring wheel rotation. The controller provides first speed signals tothe first motor that cyclically decreases and increases speed of thefirst wheel if the first amount of slip has exceeded the predeterminedfirst value of slip, and provides second speed signals to the secondmotor that cyclically decreases and increases speed of the second wheelif the second amount of slip has exceeded the predetermined second valueof slip.

In yet another aspect the invention provides a robotic device fortreating a surface wherein the robotic device includes means forreducing and/or preventing wheel slip. The robotic device includes afirst wheel driven by a first motor, a second wheel driven by a secondmotor, and a housing supported by the first wheel and the second wheel.The robotic device has means for delivering a fluid onto the surface,and means for measuring wheel rotation for the first wheel and thesecond wheel. The robotic device also has a controller in communicationwith the first motor, the second motor, the means for delivering afluid, and the means for measuring wheel rotation.

The controller receives first wheel rotation signals associated with thefirst wheel and second wheel rotation signals associated with the secondwheel from the means for measuring wheel rotation. The controllerprovides first speed signals to the first motor for driving the firstwheel and second speed signals to the second motor for driving thesecond wheel. The controller also provides fluid delivery signals to themeans for delivering a fluid.

During operation of the robotic device the controller executes a storedprogram to calculate a first amount of slip for the first wheel from thefirst wheel rotation signals received from the means for measuring wheelrotation, and calculate a second amount of slip for the second wheelfrom the second wheel rotation signals received from the means formeasuring wheel rotation. When the first amount of slip exceeds apredetermined first value of slip or the second amount of slip exceeds apredetermined second value of slip, the controller provides fluiddelivery signals to the means for delivering a fluid such that fluid isnot delivered onto the surface. In this manner, the device cantemporarily stop applying liquid floor cleaner until wheel slipsubsides.

In still another aspect, the invention provides a robotic device fortreating a surface wherein the robotic device includes means forreducing and/or preventing wheel slip. The robotic device includes afirst wheel driven by a first motor, a second wheel driven by a secondmotor, and a housing supported by the first wheel and the second wheel.The robotic device has a sheet cleaning material disposed on the device,and means for delivering a fluid onto the sheet cleaning material. Therobotic device also has means for measuring wheel rotation for the firstwheel and the second wheel.

A controller of the robotic device is in communication with the firstmotor, the second motor, the means for delivering a fluid, and the meansfor measuring wheel rotation. The controller receives first wheelrotation signals associated with the first wheel and second wheelrotation signals associated with the second wheel from the means formeasuring wheel rotation. The controller provides first speed signals tothe first motor for driving the first wheel and second speed signals tothe second motor for driving the second wheel. The controller alsoprovides fluid delivery signals to the means for delivering a fluid.

During operation of the robotic device, the controller executes a storedprogram to calculate a first amount of slip for the first wheel from thefirst wheel rotation signals received from the means for measuring wheelrotation, and calculate a second amount of slip for the second wheelfrom the second wheel rotation signals received from the means formeasuring wheel rotation. When the first amount of slip exceeds apredetermined first value of slip or the second amount of slip exceeds apredetermined second value of slip, the controller provides fluiddelivery signals to the means for delivering a fluid such that fluid isnot delivered onto the sheet cleaning material. In this manner, thedevice can temporarily stop applying liquid floor cleaner until wheelslip subsides.

Hence, a robotic device with improved anti-slip control is provided. Theforegoing and other advantages of the invention will become apparentfrom the following description. In the following description referenceis made to the accompanying drawing which forms a part thereof, and inwhich there is shown by way of illustration preferred embodiments of theinvention. These embodiments do not represent the full scope of theinvention. Reference should therefore be made to the claims herein forinterpreting the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded rear perspective view of an autonomous roboticsurface treating device of the present invention;

FIG. 2 is an exploded frontal perspective view of the device of FIG. 1;

FIG. 3 is a view similar to FIG. 1, but with upper housings removed;

FIG. 4 is a view similar to FIG. 2, but with upper housings removed;

FIG. 5 is a schematic view illustrating how a take-up reel of theassembly is ratcheted for one-way motion;

FIG. 6 is an enlarged perspective view of an end of a supply reel of thepresent assembly;

FIG. 7 is a view similar to FIG. 1, but showing the device in fullyassembled form;

FIG. 8 is a sectional view taken along line 8-8 of FIG. 7;

FIG. 9 is an enlarged view of the reel-to-reel portion of the presentdevice, highlighting a portion of the FIG. 8 drawing;

FIG. 10 is a front, left, upper perspective view of an alternativecartridge useful with the FIG. 1 device, when cleaning carpeting;

FIG. 11 is a view similar to FIG. 10, but with an upper cover removed;

FIG. 12 is a right, front, upper perspective view of a sleeve for adrive wheel for such devices (with wheel hub removed);

FIG. 13 is a front elevational view of the wheel sleeve of FIG. 12;

FIG. 14 is a side elevational view of the wheel sleeve of FIG. 12; and

FIG. 15 is a schematic comparison of two prior art modes of travel witha preferred wave mode of travel of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

We first describe example autonomous cleaning devices with reference toFIGS. 1-11. This provides examples of environments where the inventionof the present invention can be applied. Thereafter, we describe withreference to FIGS. 12-15 specific features of the present invention.

It should be understood that the present invention is also suitable foruse with many other types of autonomous treating devices. Thus, theinvention is not intended to be restricted to just cleaning devices,much less devices having the specific attributes shown in FIGS. 1-11.

Referring particularly to FIGS. 1 and 3, there is a cleaning cartridge10 suitable to be inserted into a cleaning device 12. The cleaningcartridge 10 has a roll of sheet cleaning material 44 which is providedin a reel-to-reel configuration. A portion of the roll is maintained incontact with the surface below the cleaning device 12 at any given timeduring operation. A motor 52 is provided in the cleaning device 12 toconsistently index the cleaning sheet material, so as to maintain arelatively fresh sheet against the floor.

Referring now also to FIGS. 2 and 4, the cleaning device 12 is in theform of an autonomous robot which includes a housing 13 having anaperture 14 sized and dimensioned to receive the cleaning cartridge 10.In the housing 13 and located above the aperture 14 are two windows 22and 24 which allow the user to view the cleaning cartridge 10, and theroll of cleaning sheet material 44 maintained therein.

An aperture 25 is also provided which, in conjunction with a latchingdevice 27 on the cartridge 10, provides a latch for selectivelyconnecting the cartridge 10 to the cleaning device 12. The cleaningdevice 12 also includes a bumper 15 at a front end and side brushes 16.As shown in FIG. 8, the cleaning device 12 also includes a sweeper brush60 for cleaning large particulate matter. The cleaning sheet material 44follows the brush 60 and typically cleans smaller particulate mattersuch as hair and dust which have not been picked up through the use ofthe brush 60.

The cartridge 10 includes windows 26 and 28 which, when positioned inthe cleaning device 12, are aligned with the windows 22 and 24 in thehousing 13 of the cleaning device 12, thereby allowing a user visualaccess to the cleaning sheet material 44 within the cartridge 10. A dustbin 30 is provided in the cleaning cartridge 10 at the end of thecartridge which is received inside of the housing 13 of the cleaningdevice 12.

The dust bin 30 is designed to be positioned adjacent the brush 60 (FIG.8) in the cleaning device 12. It is selectively covered by a hinged lid38, which is forced open as the cleaning cartridge 10 is moved into thecleaning device 12 but which swings shut and is therefore normallyclosed when the cartridge is removed from the cleaning device 12,thereby retaining dust collected by the cleaning device 12 within thedust bin 30 for cleaning, replacement, or disposal of the cartridge 10.

A flexible blade 32 is provided in front of the dust bin 30, directedfrom an upper edge of the dust bin 30 to the surface below the cartridge10. The flexible blade 32 directs dirt collected by the brush 60 of thecleaning device 12 into the dust bin 30.

The reel-to-reel device provided in the cartridge 10 includes both atake-up reel 34, to which used cleaning sheet material 44 is directed,and a supply reel 36, to which an unused roll of cleaning sheet materialis connected and from which the cleaning process is supplied. Thetake-up reel 34 (FIG. 5) is ratcheted in order to prevent used cleaningsheet material 44 from being directed back over the surface to becleaned, while the supply reel 36 (FIG. 6) provides a resistive forcelimiting rolling of the sheet unless driven by the stepper motor 52.Teeth 35 in the take-up reel 34 are engaged with spring-loaded teeth 33to ratchet the reel and limit motion.

The cleaning sheet material 44 can comprise, for example, anelectrostatic or electret material. Examples of such materials are thosedescribed in WO 02/00819. The cleaning sheet material 44 can alsoprovide a liquid treating or dispensation function. For example, thecleaning cloth can be treated with cleaning fluid or polishes to treatthe floor with surfactants, insecticides, insect repellants, and/orfragrances.

The cartridge 10 can further comprise a fluid reservoir 42 for providinga fluid to the cleaning sheet material 44 during operation. The fluidsupply provided in the reservoir 42 is connected to a pump 50 providedin the cleaning device 12 through fluid inlets 40 provided on thecartridge 10 and fluid outlets 48 provided on the cleaning device 12. Inoperation, therefore, the control of fluid flow to the cleaning sheetmaterial 44 is controlled by the cleaning device 12, and is provided tothe sheet material to maintain a selected level of moisture over thelife of the cartridge.

A bank of batteries 54 provides power to the cleaning device, which isselectively activated by a switch 18 (FIG. 1) provided on the cleaningdevice 12. The batteries are preferably rechargeable, and are accessedthrough a port 55 provided in the side of the housing of the cleaningdevice 12 (FIG. 2)

The cloth supply reel 36 is driven by the stepper motor 52 provided inthe cleaning device and the amount of the roll of the sheet material 44which is unwound during operation is monitored by an optical sensor 46,which is also provided in the cleaning device 12. The stepper motor 52,optical sensor 46, and pump 50 are each driven by a programmablecontroller (not shown, but positioned above the battery pack) based ontiming which drives the stepper motor to replace the sheet material asnecessary to maintain proper cleaning processes during a cleaningoperation while monitoring actual movement of the sheet.

Similarly, the controller drives the pump 50 to supply fluid to the rollof sheet material 44 as necessary during cleaning. The timing forreplenishment of the fluid source is based on the type of material andfluid being employed, and in the expected life of the roll of cleaningsheet material 44. The controller preferably maintains the cleaningsheet material 44 in a constant tension, and, while in use, indexes at apredetermined rate, as for example, 0.75 inches per 5 minutes orthereabout, over the life of the cartridge. The stepper motor 52 iscoupled to the take-up reel 34 through a series of gears, while thesupply reel is coupled to the optical sensor which detects the amount ofrotation of the supply wheel.

Referring now to FIGS. 8 and 9, the cleaning device 12 includes a beateror sweeping brush 60. A wheel 62 at the front of the cleaning device 12is adjustable by activation of a switch 20 between at least twopositions, one selected for use with a carpet, and another for use witha hard floor surface. As the cartridge 10 is inserted into the robot 12the flexible blade 32 is positioned adjacent the main brush 60 andreceives the relatively large particulate matter collected by the brushas the cleaning device 12 is run across a floor surface. Theparticulates are directed up the flexible blade 32 by the main brush 60and into the dust containment bin 30.

In operation the hinged lid 38 is retained in an open position such thatthe dust and particulate matter can be readily directed into thecontainment bin 30. Following behind the main brush 60 is the cartridge10 including the cleaning sheet material 44. The cleaning sheet material44 is retained against the surface to be cleaned by a platen 66 whichincludes a leaf-spring 64 that insures contact between the surface to becleaned and the cleaning cloth 44. Also as described above, thereservoir 42 is provided adjacent the cleaning material 44 such thatfluids can be applied to replenish the cloth when a wet or moist mopcloth is employed in the cleaning device 12.

Although a cleaning sheet material 44 has been shown and describedparticularly designed for use on a hard, smooth floor, a cartridge 10for use with a carpet is shown in FIGS. 10 and 11. Here, the cartridgecomprises a larger dust containment bin 30, and is weightedappropriately to maintain the cleaning device 12 against the surface tobe cleaned, and in an upright position during the cleaning operation.

The cartridge 10 preferably is a replaceable element that can be thrownaway as a unit when the sheet material is used up, the fluid in thefluid reservoir 42 is spent, or the dust bin is full. Furthermore, evenbefore the cleaning material is spent, the cartridge 10 can be removedand the dust bin 30 emptied by the user with minimal dust dispersion.

In an alternative embodiment (not shown), the fluid reservoir 42 candeliver fluid directly to the floor during operation. The fluid supplyprovided in the reservoir 42 is connected to the pump 50 provided in thecleaning device 12 through fluid inlets 40 provided on the cartridge 10and fluid outlets 48 provided on the cleaning device 12. The controllerdrives the pump 50 to supply fluid to the floor as necessary duringcleaning.

Turning now to key features of the present invention, the cleaningdevice 12 includes motors 70 and 71 for driving the left wheel 101 andthe right wheel 102 of the cleaning device 12, respectively. The motors70, 71 are each controlled by the programmable controller which includesa microprocessor under the control of a software program stored in amemory. Among other things, the controller provides voltage signals tothe motors 70 and 71 that cause the left wheel 101 and the right wheel102 to start, stop, rotate in a direction causing forward motion of thecleaning device 12, rotate in a direction causing reverse motion of thecleaning device 12, and rotate at increased or decreased speeds.

An encoder is associated with each wheel 101,102 and is connected to thecontroller. Encoders are commercially available and in one version, theencoder outputs a signal having a pulse every time each wheel 101,102rotates a predetermined angle. For example, an optical encoder outputspulses each time an optical beam is broken by an element that rotateswith the wheel. The controller respectively calculates the wheel speedof each wheel 101,102 based upon an interval between pulses outputtedfrom each encoder. Changes in the interval between pulses can also beused by the controller to calculate wheel acceleration.

Among other things, the controller can use calculated wheel speeds tocontrol motion of the left wheel 101 and the right wheel 102. In oneexample algorithm, the controller provides a positive voltage in therange of 0 to +10 volts to each motor 70 and 71 to drive the left wheel101 and the right wheel 102 in forward motion. The controller usescalculated wheel speeds to determine the amount of voltage to be appliedthe motors 70 and 71 to control motion of the left wheel 101 and theright wheel 102. Voltage controls the motor speed as voltage willtypically be proportional to motor speed. The controller provides anegative voltage in the range of 0 to −10 volts to each motor 70 and 71to drive the left wheel 101 and the right wheel 102 in reverse motion.

Turning next to focus on FIGS. 12-14, the tread portions of wheels areshown. These could be integral with hubs and thus suitable to linkdirectly to axles connected with the driving motors. Alternatively,these could be separate treads positioned on separate hubs.

In any event, these drawings show tread for a particular left wheel 101,which preferably will be identical to tread for the right wheel 102. Thetread of the left wheel 101 has a tread 111 having lateral grooves 113of depth 117 on each side of the tread 111. A circumferentiallongitudinal channel 115 extends around the tread 111 between thegrooved sections. The entire wheel 101 may be formed from athermoplastic styrenic material. This material provides good grip aswell as chemical resistance. In one form, the radius of the wheel 101 is31.70 millimeters, the transverse width of the wheel 101 is 23.50millimeters, the transverse width of the longitudinal channel 115 is 7.7millimeters, the depth 117 of the lateral grooves is 2.01 millimeters,and the floor contacting surfaces 116 are 1.07 millimeters in thecircumferential direction and 7.90 millimeters in the transversedirection.

During a wet cleaning operation of the autonomous floor cleaner 12, athin film of fluid is deposited on the floor surface by way of directdelivery from the fluid reservoir 42 to the floor surface or by way ofthe moistened cleaning sheet material 44. Traction is improved byreducing the thickness of the film layer to the point where tire treadand floor surface are able to make contact. In one embodiment, this isachieved as the controller of the cleaning device 12 provides fluiddelivery signals to the pump 50 such that the layer of fluid on thefloor surface has a thickness less than the depth 117 of the treadgrooves 113. In this manner, traction is improved by reducing thethickness of the fluid layer to the point where tire tread and floorsurface are able to make contact. Also, the longitudinal channel 115 ofthe tread 111 channels fluid away to further improve traction of thewheels 101, 102.

There can be an algorithm in the controller for measuring slippage ofthe left wheel 101 and/or the right wheel 102 of the cleaning device 12,whereby the controller calculates and compares wheel speeds for the leftwheel 101 and the right wheel 102. Wheel slipping results when a motordrives its wheel at too high of a speed relative to the other wheels.

Thus, if motor 70 drives the left wheel 101 at too high of a speedrelative to the right wheel 102, the controller outputs a variableindicating left wheel slippage. Likewise, if motor 71 drives the rightwheel 102 at too high of a speed relative to the left wheel 101, thecontroller outputs a variable indicating right wheel slippage. Therelative difference between left wheel speed and right wheel speed thatindicates a wheel slippage condition can be programmed in thecontroller.

In another example algorithm for measuring slippage of the left wheel101 and/or the right wheel 102 of the cleaning device 12, an encoder isprovided for the wheel 62 at the front of the cleaning device 12. Thecontroller calculates the wheel speed of wheel 62 based upon an intervalbetween pulses outputted from the encoder associated with the wheel 62.Wheel 62 is not driven by a motor and therefore, it provides a goodvalue for the forward or reverse speed of the cleaning device 12. Wheelslipping can be deemed to have resulted if motor 70 drives the leftwheel 101 at too high of a speed relative to the wheel 62 or if motor 71drives the right wheel 102 at too high of a speed relative to the wheel62. Therefore, the controller outputs variables indicating left wheelslippage or right wheel slippage based on a programmed relativedifference between the left wheel speed and the speed of the wheel 62and the right wheel speed and the speed of the wheel 62.

In still another example algorithm for measuring slippage of the leftwheel 101 and/or the right wheel 102 of the cleaning device 12, therelationship between wheel torque and slippage is used to calculatewheel slippage. Typically, under-torque conditions indicate wheelslippage. The torque on the left wheel 101 and the torque on the rightwheel 102 may be calculated as a function of current in the wheel motors70 and 71. Thus, the controller outputs variables indicating left wheelslippage or right wheel slippage based on wheel motor current readings.

Yet another example algorithm for measuring slippage of the left wheel101 and/or the right wheel 102 of the cleaning device 12 is described inU.S. Pat. No. 6,046,565 which is incorporated herein by reference alongwith all other patents cited herein.

Having calculated slippage of the left wheel 101 and/or the right wheel102, the controller executes one of the specified software routines thatreduce and/or prevent wheel slip in the autonomous floor cleaner 12. Forexample, if the software determines that the amount of wheel slip of theleft wheel 101 exceeds a predetermined first value of slip (that may beprogrammed in the controller) or that the amount of wheel slip of theright wheel 102 exceeds a predetermined second value of slip (that maybe programmed in the controller), the controller provides speed signalsto the motor 70 and provides speed signals to the motor 71 such that thedevice navigates in a side-to-side wavy pattern. This can be achieved byvarying wheel speed between the left wheel 101 and the right wheel 102.

For instance, when the speed of the right wheel 102 exceeds the leftwheel 101, the cleaning device 12 will veer left, and when the speed ofthe left wheel 101 exceeds the right wheel 102, the cleaning device 12will veer right. In FIG. 15, this wave mode for anti-slip motion isshown to the right of a conventional straight line mode and aconventional spiral mode for autonomous robot navigation. It is mostpreferred that the side-to-side motion be limited to only a fewcentimeters at most so that the algorithm will work a vertical wall.

Alternatively, if the software determines that the amount of wheel slipof the left wheel 101 exceeds a predetermined first value of slip, thecontroller provides speed signals to the motor 70 that slow or stop theleft wheel 101. The controller may also provide further speed signals tothe motor 70 that increase speed of the left wheel 101 after the leftwheel 101 has been slowed or stopped. There may be a pause period whilethe system allows some cleaner to evaporate. In any event, at some pointthe software slowly ramps up the speed to gain traction.

In yet another software routine, if the software determines that theamount of wheel slip of the left wheel 101 exceeds a predetermined firstvalue of slip, the controller provides speed signals to the motor 70that cyclically decrease and increase speed of the left wheel 101. Ifthe software determines that the amount of wheel slip of the right wheel102 exceeds a predetermined second value of slip, the controllerprovides speed signals to the motor 71 that cyclically decrease andincrease speed of the right wheel 102. In this manner, the device canmodulate wheel speed until wheel slip subsides.

In yet another software routine, if the software determines that theamount of wheel slip of the left wheel 101 exceeds a predetermined firstvalue of slip or the amount of wheel slip of the right wheel 102 exceedsa predetermined second value of slip, the controller provides fluiddelivery signals to the pump 50 such that fluid is not delivered ontothe surface. In this manner, the device can temporarily stop applyingliquid floor cleaner until wheel slip subsides.

In yet another software routine, if the software determines that theamount of wheel slip of the left wheel 101 exceeds a predetermined firstvalue of slip or the amount of wheel slip of the right wheel 102 exceedsa predetermined second value of slip, the controller provides fluiddelivery signals to the pump 50 such that fluid is not delivered ontothe sheet cleaning material 44. In this manner, the device cantemporarily stop applying liquid floor cleaner until wheel slipsubsides.

Although specific embodiments of the present invention have beendescribed in detail, it should be understood that this description ismerely for purposes of illustration. Many modifications and variationsto the specific embodiments will be apparent to those skilled in theart, which will be within the spirit and scope of the invention.Therefore, the invention should not be limited to the describedembodiments. Rather, the claims should be looked to in order to judgethe full scope of the invention.

INDUSTRIAL APPLICABILITY

Disclosed are wheel tread configurations, wave mode navigationalcontrolling systems, ramp up recovery systems, and other software forreducing and/or preventing wheel slip in an autonomous floor treaterthat applies fluid to a surface being treated.

1. A robotic device for treating a surface, comprising: a first wheelhaving a first tread and a second wheel having a second tread, the firsttread and the second tread having grooves of a depth exceeding apredetermined depth; a housing supported by the first wheel and thesecond wheel; means for delivering a layer of fluid onto the surface,and a controller in communication with the means for delivering a fluid,the controller providing fluid delivery signals to the means fordelivering a fluid such that the layer of fluid on the surface has athickness less than the predetermined depth.
 2. The device of claim 1wherein: the first tread and the second tread have a sprocket shape. 3.The device of claim 2 wherein: radial edges of the sprocket shape arerectangular.
 4. The device of claim 1 wherein: the first tread and thesecond tread have a radially extending peripheral groove.
 5. The deviceof claim 1, further comprising a pump connected to a fluid reservoir asthe means for delivering a layer of fluid onto the surface.
 6. Thedevice of claim 5, further comprising a sheet material that receives thefluid from the pump and the fluid reservoir as the means for deliveringa layer of fluid onto the surface.
 7. The device of claim 1, furthercomprising a first motor that drives the first wheel, a second motorthat drives the second wheel, and a means for measuring wheel rotationof the first wheel and the second wheel, the controller in furthercommunication with the first motor, the second motor, and the means formeasuring wheel rotation, the controller receiving first wheel rotationsignals associated with the first wheel from the means for measuringwheel rotation, the controller receiving second wheel rotation signalsassociated with the second wheel from the means for measuring wheelrotation, the controller providing first speed signals to the firstmotor for driving the first wheel, the controller providing second speedsignals to the second motor for driving the second wheel, wherein thecontroller executes a stored program to: (i) calculate a first amount ofslip for the first wheel from the first wheel rotation signals receivedfrom the means for measuring wheel rotation, (ii) calculate a secondamount of slip for the second wheel from the second wheel rotationsignals received from the means for measuring wheel rotation, (iii) whenthe first amount of slip exceeds a predetermined first value of slip orthe second amount of slip exceeds a predetermined second value of slip,provide fluid delivery signals to the means for delivering a fluid suchthat fluid is not delivered onto the surface.
 8. The device of claim 7,further comprising a pump that delivers the fluid to the surface and isin communication with the controller, and wherein when the storedprogram provides fluid delivery signals to the means for delivering afluid such that fluid is not delivered onto the surface, the controllerprovides fluid delivery signals to the pump such that the fluid is notdelivered onto the surface.
 9. The device of claim 7, further comprisinga cleaning sheet material that delivers the fluid to the surface, andwherein when the stored program provides fluid delivery signals to themeans for delivering a fluid such that fluid is not delivered onto thesurface, the controller provides fluid delivery signals such thatdelivery of the fluid onto the cleaning sheet material is stopped. 10.The device of claim 7, wherein the means for measuring wheel rotation ofthe first wheel and the second wheel is an encoder.
 11. The device ofclaim 7, wherein: the controller executes a stored program to: (iv)provide first speed signals to the first motor that slow or stop thefirst wheel, and (v) provide second speed signals to the second motorthat slow or stop the second wheel.
 12. The device of claim 10, wherein:the controller executes a stored program to: (vi) pause for a period oftime to allow some cleaner to evaporate before further providing firstspeed signals to start the first wheel or second speed signals to startthe second wheel.